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/* Optimized strlen implementation for PowerPC64/POWER8 using a vectorized
loop.
Copyright (C) 2016-2017 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
#include <sysdep.h>
/* TODO: change these to the actual instructions when the minimum required
binutils allows it. */
#define MFVRD(r,v) .long (0x7c000067 | ((v)<<(32-11)) | ((r)<<(32-16)))
#define VBPERMQ(t,a,b) .long (0x1000054c \
| ((t)<<(32-11)) \
| ((a)<<(32-16)) \
| ((b)<<(32-21)) )
/* int [r3] strlen (char *s [r3]) */
/* TODO: change this to .machine power8 when the minimum required binutils
allows it. */
.machine power7
EALIGN (strlen, 4, 0)
CALL_MCOUNT 1
dcbt 0,r3
clrrdi r4,r3,3 /* Align the address to doubleword boundary. */
rlwinm r6,r3,3,26,28 /* Calculate padding. */
li r0,0 /* Doubleword with null chars to use
with cmpb. */
li r5,-1 /* MASK = 0xffffffffffffffff. */
ld r12,0(r4) /* Load doubleword from memory. */
#ifdef __LITTLE_ENDIAN__
sld r5,r5,r6
#else
srd r5,r5,r6 /* MASK = MASK >> padding. */
#endif
orc r9,r12,r5 /* Mask bits that are not part of the string. */
cmpb r10,r9,r0 /* Check for null bytes in DWORD1. */
cmpdi cr7,r10,0 /* If r10 == 0, no null's have been found. */
bne cr7,L(done)
/* For shorter strings (< 64 bytes), we will not use vector registers,
as the overhead isn't worth it. So, let's use GPRs instead. This
will be done the same way as we do in the POWER7 implementation.
Let's see if we are aligned to a quadword boundary. If so, we can
jump to the first (non-vectorized) loop. Otherwise, we have to
handle the next DWORD first. */
mtcrf 0x01,r4
mr r9,r4
addi r9,r9,8
bt 28,L(align64)
/* Handle the next 8 bytes so we are aligned to a quadword
boundary. */
ldu r5,8(r4)
cmpb r10,r5,r0
cmpdi cr7,r10,0
addi r9,r9,8
bne cr7,L(done)
L(align64):
/* Proceed to the old (POWER7) implementation, checking two doublewords
per iteraction. For the first 56 bytes, we will just check for null
characters. After that, we will also check if we are 64-byte aligned
so we can jump to the vectorized implementation. We will unroll
these loops to avoid excessive branching. */
ld r6,8(r4)
ldu r5,16(r4)
cmpb r10,r6,r0
cmpb r11,r5,r0
or r5,r10,r11
cmpdi cr7,r5,0
addi r9,r9,16
bne cr7,L(dword_zero)
ld r6,8(r4)
ldu r5,16(r4)
cmpb r10,r6,r0
cmpb r11,r5,r0
or r5,r10,r11
cmpdi cr7,r5,0
addi r9,r9,16
bne cr7,L(dword_zero)
ld r6,8(r4)
ldu r5,16(r4)
cmpb r10,r6,r0
cmpb r11,r5,r0
or r5,r10,r11
cmpdi cr7,r5,0
addi r9,r9,16
bne cr7,L(dword_zero)
/* Are we 64-byte aligned? If so, jump to the vectorized loop.
Note: aligning to 64-byte will necessarily slow down performance for
strings around 64 bytes in length due to the extra comparisons
required to check alignment for the vectorized loop. This is a
necessary tradeoff we are willing to take in order to speed up the
calculation for larger strings. */
andi. r10,r9,63
beq cr0,L(preloop)
ld r6,8(r4)
ldu r5,16(r4)
cmpb r10,r6,r0
cmpb r11,r5,r0
or r5,r10,r11
cmpdi cr7,r5,0
addi r9,r9,16
bne cr7,L(dword_zero)
andi. r10,r9,63
beq cr0,L(preloop)
ld r6,8(r4)
ldu r5,16(r4)
cmpb r10,r6,r0
cmpb r11,r5,r0
or r5,r10,r11
cmpdi cr7,r5,0
addi r9,r9,16
bne cr7,L(dword_zero)
andi. r10,r9,63
beq cr0,L(preloop)
ld r6,8(r4)
ldu r5,16(r4)
cmpb r10,r6,r0
cmpb r11,r5,r0
or r5,r10,r11
cmpdi cr7,r5,0
addi r9,r9,16
bne cr7,L(dword_zero)
andi. r10,r9,63
beq cr0,L(preloop)
ld r6,8(r4)
ldu r5,16(r4)
cmpb r10,r6,r0
cmpb r11,r5,r0
or r5,r10,r11
cmpdi cr7,r5,0
addi r9,r9,16
/* At this point, we are necessarily 64-byte aligned. If no zeroes were
found, jump to the vectorized loop. */
beq cr7,L(preloop)
L(dword_zero):
/* OK, one (or both) of the doublewords contains a null byte. Check
the first doubleword and decrement the address in case the first
doubleword really contains a null byte. */
cmpdi cr6,r10,0
addi r4,r4,-8
bne cr6,L(done)
/* The null byte must be in the second doubleword. Adjust the address
again and move the result of cmpb to r10 so we can calculate the
length. */
mr r10,r11
addi r4,r4,8
/* If the null byte was found in the non-vectorized code, compute the
final length. r10 has the output of the cmpb instruction, that is,
it contains 0xff in the same position as the null byte in the
original doubleword from the string. Use that to calculate the
length. */
L(done):
#ifdef __LITTLE_ENDIAN__
addi r9, r10,-1 /* Form a mask from trailing zeros. */
andc r9, r9,r10
popcntd r0, r9 /* Count the bits in the mask. */
#else
cntlzd r0,r10 /* Count leading zeros before the match. */
#endif
subf r5,r3,r4
srdi r0,r0,3 /* Convert leading/trailing zeros to bytes. */
add r3,r5,r0 /* Compute final length. */
blr
/* Vectorized implementation starts here. */
.p2align 4
L(preloop):
/* Set up for the loop. */
mr r4,r9
li r7, 16 /* Load required offsets. */
li r8, 32
li r9, 48
li r12, 8
vxor v0,v0,v0 /* VR with null chars to use with
vcmpequb. */
/* Main loop to look for the end of the string. We will read in
64-byte chunks. Align it to 32 bytes and unroll it 3 times to
leverage the icache performance. */
.p2align 5
L(loop):
lvx v1,r4,r0 /* Load 4 quadwords. */
lvx v2,r4,r7
lvx v3,r4,r8
lvx v4,r4,r9
vminub v5,v1,v2 /* Compare and merge into one VR for speed. */
vminub v6,v3,v4
vminub v7,v5,v6
vcmpequb. v7,v7,v0 /* Check for NULLs. */
addi r4,r4,64 /* Adjust address for the next iteration. */
bne cr6,L(vmx_zero)
lvx v1,r4,r0 /* Load 4 quadwords. */
lvx v2,r4,r7
lvx v3,r4,r8
lvx v4,r4,r9
vminub v5,v1,v2 /* Compare and merge into one VR for speed. */
vminub v6,v3,v4
vminub v7,v5,v6
vcmpequb. v7,v7,v0 /* Check for NULLs. */
addi r4,r4,64 /* Adjust address for the next iteration. */
bne cr6,L(vmx_zero)
lvx v1,r4,r0 /* Load 4 quadwords. */
lvx v2,r4,r7
lvx v3,r4,r8
lvx v4,r4,r9
vminub v5,v1,v2 /* Compare and merge into one VR for speed. */
vminub v6,v3,v4
vminub v7,v5,v6
vcmpequb. v7,v7,v0 /* Check for NULLs. */
addi r4,r4,64 /* Adjust address for the next iteration. */
beq cr6,L(loop)
L(vmx_zero):
/* OK, we found a null byte. Let's look for it in the current 64-byte
block and mark it in its corresponding VR. */
vcmpequb v1,v1,v0
vcmpequb v2,v2,v0
vcmpequb v3,v3,v0
vcmpequb v4,v4,v0
/* We will now 'compress' the result into a single doubleword, so it
can be moved to a GPR for the final calculation. First, we
generate an appropriate mask for vbpermq, so we can permute bits into
the first halfword. */
vspltisb v10,3
lvsl v11,r0,r0
vslb v10,v11,v10
/* Permute the first bit of each byte into bits 48-63. */
VBPERMQ(v1,v1,v10)
VBPERMQ(v2,v2,v10)
VBPERMQ(v3,v3,v10)
VBPERMQ(v4,v4,v10)
/* Shift each component into its correct position for merging. */
#ifdef __LITTLE_ENDIAN__
vsldoi v2,v2,v2,2
vsldoi v3,v3,v3,4
vsldoi v4,v4,v4,6
#else
vsldoi v1,v1,v1,6
vsldoi v2,v2,v2,4
vsldoi v3,v3,v3,2
#endif
/* Merge the results and move to a GPR. */
vor v1,v2,v1
vor v2,v3,v4
vor v4,v1,v2
MFVRD(r10,v4)
/* Adjust address to the begninning of the current 64-byte block. */
addi r4,r4,-64
#ifdef __LITTLE_ENDIAN__
addi r9, r10,-1 /* Form a mask from trailing zeros. */
andc r9, r9,r10
popcntd r0, r9 /* Count the bits in the mask. */
#else
cntlzd r0,r10 /* Count leading zeros before the match. */
#endif
subf r5,r3,r4
add r3,r5,r0 /* Compute final length. */
blr
END (strlen)
libc_hidden_builtin_def (strlen)
|
